The broad objectives of this program are to explore the molecular basis and physiological functions of ion transport in microorganisms. There is now strong evidence that in bacteria the linkage between metabolism and transport is usually indirect, effected by a circulation of protons across the cytoplasmic membrane (chemiosmotic theory). At the same time we have come to recognize a second major class of transport systems that are energized by a phosphoryl donor, possible ATP. Indeed, some important systems including those for K ion, Na ion, and Pi- require both ATP and the proton circulation. We are studying the molecular basis of ATP-linked transport, its interaction with the proton circulation and its significance in the economy of bacterial cells. We shall employ both intact cells and membrane vesicles of Streptococcus faecalis, an organism that offers technical as well as conceptual advantages. Future plans include initiation of a parallel program with eukaryotic fungi.